7.3.9 DC Detect Protection

The TPA31xxD2 has circuitry which will protect the speakers from DC current which might occur due to defective capacitors on the input or shorts on the printed circuit board at the inputs. A DC detect fault will be reported on the FAULT pin as a low state. The DC Detect fault will also cause the amplifier to shutdown by changing the state of the outputs to Hi-Z.

If automatic recovery from the short circuit protection latch is desired, connect the FAULTZ pin directly to the SDZ pin. Connecting the FAULTZ and SDZ pins allows the FAULTZ pin function to automatically drive the SDZ pin low which clears the DC Detect protection latch.

A DC Detect Fault is issued when the output differential voltage of either channel exceeds DC protection threshold level for more than 640 ms at the same polarity. Table 5 below shows some examples of the typical DC Detect Protection threshold for several values of the supply voltage. The Detect Protection Threshold feature protects the speaker from large DC currents or AC currents less than 2 Hz. To avoid nuisance faults due to the DC detect circuit, hold the SD pin low at power-up until the signals at the inputs are stable. Also, take care to match the impedance seen at the positive and negative inputs to avoid nuisance DC detect faults.

Table 5 lists the minimum output offset voltages required to trigger the DC detect. The outputs must remain at or above the voltage listed in the table for more than 640 ms to trigger the DC detect.